1. Field of the Invention
The invention relates to a dosing device for quantitative dosing of small amounts of liquids, comprising a body, a flexible bellows attached to the body defining a liquid space, a dosing tip communicating with the liquid space, and an actuator for moving the bellows to provide a constriction of the liquid space causing a liquid dose to be discharged from the dosing tip.
The invention further relates to methods for dosing small amounts of liquids quantitatively by means of flexible bellows moved by an actuator, and a dosing tip communicating with the bellows.
2. Description of the Prior Art
In conventional liquid dosing devices, a piston moving in a cylinder is used as the actuator to discharge a liquid dose. Main drawbacks of such dosing devices are the sliding friction between the cylinder and the piston and unpreciseness of the setting in motion and stopping of the piston, and as a consequence, reproducibility required in precise dosing of small liquid doses is not assured.
Published specification FI 94675 discloses a dispenser comprising a liquid space formed by flexible bellows actuated by an actuator. In this specification, the actuator is a stepping motor connected to the bellows through a gyrating shaft or a piezo rod or servo motor acting directly on the bellows. Substantial advantage of the described solution over a piston moving in a cylinder is the fact that the bellows may be moved without sliding friction in the mechanical parts. According to this publication, the bellows draw liquid through the dosing tip to the liquid space of the dispenser, and then, in the dosing step, a liquid dose is discharged from the dosing tip dipped into another liquid receiving said dose by moving the bellows in opposite direction.
In the dispenser described as an example in publication FI 94675, the volume change of the bellows produced in one step of the stepping motor serving as the actuator was about 10 μl. being theoretically the smallest liquid amount that may be dosed in this case. The stepping motor has a high number of step positions, and when dosing liquid volumes larger than said minimum volume, the motor is not able to pass direction from one step position to the other, but must pass through several successive steps with a defined velocity change in each step interval. This in turn limits the acceleration and slowing down of the dosing movement found to have a substantial role in dosing very small liquid doses according to the invention. This publication presents no description of dosing liquid amounts of nanoliter order, nor dosing droplets wherein liquid is discharged from the dosing tip into the air one droplet at a time.
A servo motor or a piezo rod acting as an actuator is not described in publication FI 94675 as fully as the stepping motor connected to the bellows through a shaft. However, the same limitations with respect to the acceleration of the movement apply both to the servo motor and to the stepping motor. Particularly, a drawback of the piezo rod is in turn the fact that a long piezo rod and high voltage source dangerous to the user are needed for the path of the bellows required in dosing a high number of liquid doses successively. In this case, the masses of the rod and moving auxiliary devices as well as the operation time thereof also become an obstruction to the sufficient acceleration of the movement.
Dosing liquid doses through the air from a dosing tip moved by bellows is known as such from FI104891. This document relates to serial dosing of liquid doses into packings by drawing liquid into the suction tip with bellows, followed by filling the packings one at a time by means of opposite dosing movements of the bellows. In contrast to FI94675, liquid is only present in the dosing tip whereas the bellows are filled with air. As stated in this publication, the preciseness attained with this technique is not too high, only about 1 percent, the volume of the doses to be dosed being from 5-500 μl according to said publication. Thus, said publication teaches no solution enabling the precision dosing of liquid amounts of nanoliter order.
In printers, it is known to use a technique using discharging an ink jet as droplets with the volume of picoliter order. The technique is however based on the fact that several successive droplets are focused on the same point, the size of individual droplets being not precisely controlled. The technique applied in printers is not a suitable solution to quantitative dosing of liquids.
The disadvantage of the prior art is thus the lack of a technique enabling the quantitative dosing of liquid amounts measuring only nanoliters. Such a technique is not known in dosing of liquids using a dosing tip to be contacted with the surface of the receiving liquid or dipped therein to discharge the dosed amount directly into said receiving liquid, not to mention in techniques for dosing liquids by discharging small droplets thereof into the air. The object of the invention is to find a solution eliminating said drawbacks. The invention particularly provides a new dosing technique suitable for the dosing needs in the fields of biochemistry, such as clinical and environmental chemistry.